The present invention relates to the measurement of the flow of air in an air flow system, and is particularly concerned with providing more accurate measurement of the flow of air.
This invention also relates to an air volume regulator for use in an air conditioning system, and to providing more effective control over the regulation of air flow by obtaining a more accurate measurement of the air flow.
The type of air volume regulator with which the present invention may be employed has an air flow sensor mounted in the air flow for sensing the velocity of the air flowing through the regulator. The sensor is connected to a suitable control mechanism, which in turn, is connected to a damper mechanism. The damper mechanism is adjustably positioned in response to the air velocity sensed by the sensor so that the air flow discharged from the regulator is maintained at a substantially uniform volumetric flow rate regardless of variations in the pressure of the air being supplied to the air volume regulator.
Under ideal conditions, it would be desirable that the connecting duct supplying air to the air volume regulator be straight for a considerable length upstream of the regulator to establish a uniform, symmetrical air velocity distribution or profile within the connecting duct. This would insure that the air velocity measurement obtained by the air sensor would be representative of the air velocity conditions existing throughout the cross section of the duct.
Under the conditions which actually exist in field installations however, the connecting duct normally must undergo a number of bends or turns in leading from the main air supply duct to the individual air volume regulator. These bends and turns frequently produce a distorted, asymmetrical velocity distribution within the connecting duct which causes the air flow sensor to obtain an inaccurate measurement of the air flow in the duct and which results in inaccuracies in the regulation of the air flow.
The prior art has recognized the problem produced by flow disturbances and uneven velocity distributions upstream from a fluid flow sensor and the difficulty in obtaining an accurate flow measurement. Generally, the prior art has addressed this problem by mounting various types of stationary flow straighteners upstream from the flow sensor. Stationary flow straighteners have been proposed in the form of vanes, tubes, honeycomb elements, perforated plates, etc. By way of example, reference may be made to Preston U.S. Pat. No. 2,706,409; Sprenkle U.S. Pat. No. 2,929,248; and Goulet U.S. Pat. No. 3,981,193.
The prior types of stationary flow straighteners of which applicants are aware have a number of limitations which render them unsuited, or of limited usefulness, in air conditioning duct systems, and in particular in air volume regulator installations. For example, certain types of stationary flow straighteners must be mounted a considerable distance upstream from the flow sensor. This requires that the flow straightener either be mounted in the duct separately from the air volume regulator, or requires an undesirably large size regulator. Many of the known types of flow straighteners produce a significant flow obstruction and an undesirably high pressure drop which is unacceptable in many air conditioning installations. Further, because of the various ways in which air volume regulators can be installed and the various bends and turns which may be present in the upstream connecting duct, the velocity distribution of the air supplied to the regulator is completely unpredictable and the known stationary types of flow straighteners cannot take into account this unpredictability of the velocity profile.